Television – Camera – system and detail – Solid-state image sensor
Reexamination Certificate
1998-09-30
2003-11-18
Garber, Wendy R. (Department: 2612)
Television
Camera, system and detail
Solid-state image sensor
C348S308000, C348S245000
Reexamination Certificate
active
06650369
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image sensing apparatus, a signal detection apparatus, and a signal accumulation apparatus and, more particularly, to read control of a signal from a pixel or cell.
2. Related Background Art
FIGS. 1A and 1B
are equivalent circuit diagrams, respectively, showing the pixel portions of conventional two-dimensional solid-state image sensing apparatuses. In
FIGS. 1A and 1B
, the circuits respectively comprise power supply lines
1
, reset switch lines
2
, selection switch lines
3
, signal output lines
4
, and photodiodes
5
. The circuit in
FIG. 1A
also includes a transfer switch line
6
.
FIG. 1A
shows the circuit of the solid-state image sensing apparatus reported by Eric R. Fossum et al., IEDM, 1993 (technical reference 1: IEDM 93, pp. 583-586).
FIG. 1B
shows the circuit of the solid-state image sensing apparatus reported in “ISSCC96/Session 1/Plenary Session/Paper TA1.2”.
FIG. 2
shows an example of the circuit in
FIG. 1B
in which pixels are two-dimensionally laid out, and a read circuit for reading out an image signal is added.
Such a two-dimensional solid-state image sensor including a signal amplifier within each pixel requires a plurality of switch elements and a plurality of elements constituting the signal amplifier in addition to the photodiode. In
FIG. 1A
, one pixel requires one photodiode and four MOS transistors, inevitably increasing the size of one pixel.
The basic operation of the circuit in
FIGS. 1A and 2
will be described.
(1) A reset operation of inputting the reset voltage to the input node of a source follower Q
3
is performed by a reset switch Q
2
, and a row is selected by a selection switch Q
4
.
(2) The input node of the source follower Q
3
is floated. A noise component made up of reset noise and fixed pattern noise such as variations in threshold voltage of the MOS source follower Q
3
is read out, and the readout information is temporarily held in a signal accumulator
15
.
(3) A transfer switch Q
1
is opened/closed to transfer an accumulation charge generated by an optical signal to the input node of the source follower Q
3
. The sum of the noise component and the optical signal component is read out and held in the signal accumulator
15
.
(4) The signal of the noise component and the signal of the noise and optical signal components are respectively read out to common signal lines
19
and
19
′ via common signal line transfer switches
18
and
18
′. Outputs from the common signal lines
19
and
19
′ respectively yield outputs
13
and
14
via buffer amplifiers. In the next stage, the reset noise and the fixed pattern noise can be removed by calculating the difference between the outputs
13
and
14
. Note that pixels are sequentially scanned by a vertical shift register
12
and a horizontal shift register
16
.
To the contrary, in
FIG. 1B
, one pixel requires one photodiode and three MOS transistors. The number of transistors is smaller by one than in
FIG. 1A
, and the transfer switch line can be eliminated. This significantly reduces the pixel size.
However, owing to the absence of the transfer switch, the pixel of
FIG. 1B
does not comprise the mechanism of holding the noise component of each pixel during the accumulation period. Accordingly, noise cannot be removed, and the signal component-to-noise component ratio, i.e., S/N ratio of the image sensing apparatus is lower than in FIG.
1
A.
As described above, in the prior arts, it is difficult to realize a high S/N ratio and reduce the pixel size. In addition, the dynamic range narrows upon voltage drop of the selection switch Q
4
.
SUMMARY OF THE INVENTION
It is an object of the present invention to reduce the size of a pixel or cell.
It is another object of the present invention to prevent a decrease in dynamic range of the pixel.
To achieve the above objects, according to an embodiment of the present invention, there is provided an image sensing apparatus comprising a plurality of pixels each including photoelectric conversion means, amplification means for amplifying a signal from the photoelectric conversion means, transfer means for transferring the signal from the photoelectric conversion means to the amplification means, and read control means for controlling a read of the signal from the amplification means under control of a voltage level of an input portion of the amplification means.
According to another embodiment, there is provided a signal detection apparatus comprising a plurality of cells each including detection means, amplification means for amplifying a signal from the detection means, transfer means for transferring the signal from the detection means to the amplification means, and read control means for controlling a read of the signal from the amplification means under control of a voltage level of an input portion of the amplification means.
According to still another embodiment, there is provided a signal accumulation apparatus comprising a plurality of cells each including accumulation means, amplification means for amplifying a signal from the accumulation means, transfer means for transferring the signal from the detection means to the accumulation means, and read control means for controlling a read of the signal from the amplification means under control of a voltage level of an input portion of the amplification means.
With the above arrangement, the size of the pixel or cell can be reduced.
The pixel can attain a wide dynamic range.
Other objects and features of the present invention will be apparent from the following description in conjunction with the accompanying drawings.
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patent: 0 905 788 (1999-03-01), None
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B. Ackland et al., “Camera on a Chip”, IEEE International Solid-State circuits Conference, Feb. 8, 1996, pp. 22-25.
S. Mendis et al., “A 128 × 128 CMOS Active Pixel Image Sensor for Highly Integrated Imaging Systems”, IEEE International Electron Devices Meeting Tech. Digest, Dec. 1993.
Kochi Tetsunobu
Koizumi Toru
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Garber Wendy R.
Ye Lin
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